How do mercury(II) compounds differ from mercury(I) compounds?

Mercury compounds exist in two primary oxidation states, +1 and +2, which exhibit distinct chemical behaviors.12

Key Differences

• Bonding Nature: Mercury(II) compounds are typically covalent, whereas common salts of mercury(I) are ionic.2
• Ionic Structure: The mercury(I) ion, ${\text{Hg}}_2^{2+}$, is diatomic, featuring a covalent bond between the two metal atoms. In contrast, the mercury(II) ion is ${\text{Hg}}^{2+}$.12
• Complex Formation: The ${\text{Hg}}^{2+}$ ion readily forms complex ions, while the ${\text{Hg}}_2^{2+}$ ion shows little tendency to do so.2
• Solubility and Properties: Because mercury(I) salts are ionic, soluble compounds like mercurous nitrate, ${\text{Hg}}_2({\text{NO}}_3{)}_2$, exhibit standard properties of ionic substances, such as ease of dissociation in solution.2

Mercury(II) compounds, such as mercuric chloride (${\text{HgCl}}_2$) and mercury(II) oxide, are more prevalent than mercury(I) compounds. While mercury(I) chloride (calomel) has historically been used in antiseptic salves, mercury(II) compounds are widely utilized in the chemical industry as catalysts and in various industrial and medical applications.1